It is known in the art of emulsion polymerization that both cationic and amphoteric latices can be prepared in a highly acidic medium. U.S. Pat. No. 3,399,159 discloses a process for preparing cationic latices whereby a nitrogen-containing monomer, such as vinyl-pyridine or tertbutylaminoethyl methacrylate is polymerized, with an alkyl acrylic ester, in the absence of an emulsifier and in a medium with a pH of between 1 to 3.5, thereby forming an aqueous dispersion. A diene is then polymerized in the resultant aqueous dispersion.
It is also known that such latices can be prepared by neutralizing the initial polymerized product. U.S. Pat. No. 3,404,114 discloses the preparation of amphoteric latices by (1) polymerizing an unsaturated carboxylic acid and an unsaturated acid ester, (2) neutralizing the medium to a pH of approximately 7 with a nitrogen-containing neutralizing agent, and (3) polymerizing in the medium an alkylaminoalkyl ester of an unsaturated carboxylic acid.
Cationic and amphoteric latices prepared by emulsion polymerization have been increasingly used as binders in exterior and interior paints, as well as for foams and coatings, and thus simpler and more efficient processes for producing such latices have been attempted. It is therefore the object of the present invention to prepare stable amphoteric aqueous dispersions of copolymers based on conjugated dienes at any pH and without an intermediate neutralization step.